Sounds like a fairly typical reaction for the circumstances.
I suggest reading through some of the personal blogs.
There's a LOT regarding how to deal with jealousy/fear/insecurity in my personal blog.
Also-search those words here and you will fins many posts and threads.

Morethantwo.com has GREAT info.
Also the seven levels of intimacy ( not about poly) is VERY helpful in managing relationship communication.
Loving More by Deborah Anapol (aboit poly) is excellent for a newbie who isnt poly oriented.